# Confused .... y=x-|x|

by mikebc
Tags: confused, yx|x|
 P: 20 The problem is to graph this equation y=x-|x|. From what I understand of absolute values, this x would be positive. If it is positive then y=0 and there would be no points to graph. Is there something that I am missing? The question is worth 4 points, so I can't see the answer just being 0. Thanks for any suggestions.
 Mentor P: 15,201 What happens when x is negative?
 P: 88 What I was taught to do when dealing with absolute value, is to rewrite the equation so that the absolute value is isolated, then find the 2 equations. so you'll have: x=x-y y=o and also: x=-x+y 2x=y
 P: 20 Confused .... y=x-|x| The absolute value of -x would be x. But I remember with inequalities there are 2 possible answers with absolute value (-,+). From what you are explaining it sounds like that is what you are saying to do, use both possible values. Then I would graph by beginning with y at 0 and continue by substituting values into 2x=y? That seems to make sense to me. Thank you both for your help!
 P: 641 Also just try plugging in some numbers: For 2 -> Y = 2 - |2| = 0 For -2 - > Y = -2 -|-2| = -2 -2 = -4 see? So for negatives you have Y = 2X, X<0
 HW Helper PF Gold P: 2,841 Solve or graph y = x - |x|. If x>0, then y = x - x, meaning y=0. If x<0, then y = x - (-x) [ notice those are parentheses, not absolute value notation symbols ], meaning y = x + x = 2x.
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 Quote by mikebc The problem is to graph this equation y=x-|x|. From what I understand of absolute values, this x would be positive.
Surely you didn't mean to say that! x itself can be any number. |x| is always positive (or 0- don't forget that!

 Quote by dranseth What I was taught to do when dealing with absolute value, is to rewrite the equation so that the absolute value is isolated, then find the 2 equations. so you'll have: x=x-y y=o
Why did you switch to x=? If x$\ge 0$ y= x- x= 0. The graph is just the x axis from x= 0 to the right.

 and also: x=-x+y 2x=y
If x< 0, don't forget that. Then y= x- (-x)= 2x.

 Quote by mikebc The absolute value of -x would be x.
No, no, no! |-x|= |x| which may be eigther x or -x depending upon what x is.

 But I remember with inequalities there are 2 possible answers with absolute value (-,+). From what you are explaining it sounds like that is what you are saying to do, use both possible values. Then I would graph by beginning with y at 0 and continue by substituting values into 2x=y? That seems to make sense to me. Thank you both for your help!
Draw the graph of y= 2x, to the left of x= 0. To the right, the graph is just y= 0, the x-axis.
 P: 88 I rearranged the formula to isolate the absolute value.
 P: 20 Wow, you guys couldn't have made it any more clear for me. Thanks alot!

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